The present invention relates to a pressure-responsive actuator, and particularly to an improvement in a pressure-responsive actuator in which the inside of a case is divided into first and second air chambers by a diaphragm having a peripheral edge clamped to the case; a coil spring is accommodated in the second air chamber for exerting a spring force for urging the diaphragm in a direction to decrease the volume of the first air chamber; and a rod is coaxially connected at one of opposite ends to a side of a retainer mounted to a central portion of the diaphragm on the side of the first air chamber and at the other end to a tip end of an arm fixed at its base end to a driven shaft rotatable about an axis perpendicular to a plane parallel to the rod.
Conventionally, such a pressure-responsive actuator is known, for example, from Japanese Patent Application Laid-open No. 11-93906.
In the structure in which the rod coaxially connected at one end to the retainer mounted at the central portion of the diaphragm is connected at the other end to the tip end of the arm fixed at its base end to the rotatable driven shaft, the rod reciprocates in a longitudinal direction, while being tiled about an axis parallel to the axis of the drive shaft. The conventionally known pressure-responsive actuator is constructed to allow tilt of the rod.
In the conventional actuator, however, when the diaphragm is flexed toward the first air chamber by the spring force of the coil spring by eliminating a difference in pressure between the first and second air chamber, the rod may be tilted until the diaphragm is pushed strongly against an inner surface of the case, whereby friction is generated between the inner surface of the case and the diaphragm by the movement of the rod in the longitudinal direction, because the tilt of the rod is permitted. If such friction is generated, the diaphragm is worn, resulting in a reduction in its durability.
Accordingly, it is an object of the present invention to provide a pressure-responsive actuator which can prevent the wear of the diaphragm to enhance the durability thereof.
To achieve the above object, according to the present invention, there is provided a pressure-responsive actuator in which the inside of a case is divided into first and second air chambers by a diaphragm having a peripheral edge clamped to the case wherein a coil spring is accommodated in the second air chamber for exerting a spring force for urging the diaphragm in a direction to decrease the volume of the first air chamber; and a rod is coaxially connected at one of opposite ends to a side of a retainer mounted to a central portion of the diaphragm on the side of the first air chamber and at the other end to a tip end of an arm fixed at its base end to a driven shaft rotatable about an axis perpendicular to a plane parallel to the rod, and wherein the case is provided with a tilt-restricting portion for restricting the tilt of the rod in the plane to a range in which the contacting of the diaphragm with the inner surface of the case can be avoided.
With this arrangement, the tilt of the rod is restricted, so that the diaphragm is prevented from being brought into contact with the inner surface of the case. Therefore, the friction cannot be generated between the inner surface of the case and the diaphragm by the movement of the rod in the longitudinal direction and hence, it is possible to prevent the wear of the diaphragm to enhance the durability thereof.
In a preferred feature, at least one of the case, the retainer and the rod is made of a synthetic resin. This arrangement makes it possible to provide a reduction in weight of the pressure-responsive actuator.
In a further preferred feature, the case and the rod are made of the same synthetic resin. This arrangement enables a reduction in weight of the pressure-responsive actuator and prevents only one of the tilt-restricting portion provided on the case and the rod from being worn due to the contact between the tilt-restricting portion and the rod.
In a further preferred feature, the rod is integrally connected at one end to the retainer. This arrangement can reduce the number of parts.
In a further preferred feature, the case is mounted to an intake manifold which is constructed so that the length of an intake passageway can be varied in response to the turning of a switching valve which is turnable along with the driven shaft. With this arrangement, the switching valve included in the intake manifold can be driven for switching by the pressure-responsive actuator having a simple structure and an enhanced durability.
In a further preferred feature, the intake manifold is made of a synthetic resin. With this arrangement, a load acting on the pressure-responsive actuator for actuating the switching valve, increases due to an error in shape of the intake manifold which is likely to be caused by the intake manifold being made of the synthetic resin, whereby the rod is tend to be tilted more easily. Because the tilt of the rod is restricted as described above, however, the pressure-responsive actuator can be used more effectively.
In a further preferred feature, the switching valve is made of a synthetic resin. With this arrangement, a load acting on the pressure-responsive actuator for actuating the switching valve, increases due to an error in shape of the switching valve which is likely to be caused by the switching valve being made of the synthetic resin, whereby the rod is tend to be tilted more easily. Because the tilt of the rod is restricted as described above, however, the pressure-responsive actuator can be used more effectively.
In a further preferred feature, the switching valve is constructed into a rotary type. With this arrangement, the resistance to the sliding of the switching valve is large because of the rotary type, and the load acting on the pressure-responsive actuator increases, whereby the rod is tend to be tilted more easily. Because the tilt of the rod is restricted as described above, however, the pressure-responsive actuator can be used more effectively.
In a further preferred feature, for rotatable connection between the arm and the rod made of a synthetic resin, the arm has a pillow ball provided thereon; the rod is provided at the other end thereof with a fitting bore having at its intermediate portion an annular recess for supporting the pillow ball, and the rod has a plurality of notches provided therein to be open at least in a side of the fitting bore to which the pillow ball is fitted, the notches leading to the fitting bore at a plurality of circumferential points in the fitting bore. With this arrangement, when the pillow ball is fitted into the fitting bore, while temporarily deforming a portion of the rod, a stress acting on the rod around the fitting bore is alleviated by the presence of the plurality of notches, and the need for a special treatment such as a rod-warming treatment can be eliminated. As a result, the number of assembling steps for rotatably connecting the arm and the rod to each other can be reduced, so that the assembling operation is facilitated.
In a further preferred feature, first notch, second and third notches are provided in the other end of the rod to extend radially from the fitting bore, the first notch extending in a longitudinal direction of the rod, the second and third notches being disposed at locations where they are spaced at the same distance apart from the first notch, and the second and third notches being defined to have a length shorter than that of the first notch. With this arrangement, the first notch can be defined to have a sufficiently large length, and a sufficient number of notches can be provided in the rod, while avoiding an enlargement in end size of the rod. In addition, the stress acting on the rod around the fitting bore can be alleviated sufficiently.
In a further preferred feature, a cover portion is integrally provided on a portion of the case and fastened to the intake manifold so as to cover a connection between the rod and the driven shaft, and among a plurality of bolts for fastening the cover portion to the intake manifold, a pair of bolts are disposed at locations where the rod is interposed between the driven shaft and the diaphragm.
With this arrangement, the cover portion is integrally provided on a portion of the case so as to cover the connection between the rod and the driven shaft, and is fastened to the intake manifold. Therefore, the actuator can be fixed to and supported on the intake manifold with a reduced number of parts. Moreover, among the plurality of bolts for fastening the cover portion to the intake manifold, the pair of bolts are disposed at locations where the rod is interposed between the driven shaft and the diaphragm. Therefore, even if the actuator having a relatively large weight is disposed to protrude from the cover portion mounted to the intake manifold, it is possible to inhibit, to the utmost, that the vibration due to the oscillation of the actuator acts on the cover portion, and it is possible to prevent the vibration due to the oscillation of the actuator from exerting an adverse effect to the detection accuracy of a detector.
In a further preferred feature, the cover portion is fastened to the intake manifold through a mounting plate interposed between the cover portion and the intake manifold, and a detector housing of a detector for detecting the rotated position of the driven shaft is mounted to the cover portion. With such arrangement, the case having the cover portion, the detector and the mounting plate can be previously assembled together as a unit, and the unit can be mounted to the intake manifold, whereby the assembling operation is facilitated.